Solid-state and solution studies of tungsten(VI) organoimidoalkoxides

Abstract

The arylimidoalkoxides, [W(NC₆H₄Me-4)(OR)₄](R = Me or Prⁱ) have been shown by X-ray diffraction studies to adopt binuclear, alkoxide-bridged structures in the solid state. The alkoxide bridges are asymmetric [2.072(7) and 2.181(6)Å, R = Me; 2.029(4) and 2.243(3)Å, R = Prⁱ] and coplanar with the terminal arylimido ligands, the longer W–O bonds being trans to the short WN bonds [1.749(8)Å, R = Me; 1.738(4)Å, R = Prⁱ]. Proton NMR studies show that these structures are dynamic in solution, although much less so than their oxo analogues. The bimetallic imidoalkoxide, [{W(NC₆H₄Me-4)(OC₆H₁₁)₅Li₂Cl(C₆H₁₁OH)}₂]·C₆H₁₁OH, obtained from an attempted preparation of [W(NC₆H₄Me-4)(OC₆H₁₁)₄], has been shown by a single-crystal X-ray diffraction study to have a dimeric structure analogous to the known rhenium oxoisopropoxide, [{ReO(OPrⁱ)₅Li₂Cl(thf)}₂]·2thf (thf = tetrahydrofuran). A tungsten(V) imidochloroalkoxide, [NBuⁿ₄][W₂(NPh)₂(µ-OMe)(µ-Cl)₂Cl₄] has also been crystallographically characterised and has a distorted confacial bioctahedral structure in which one of the bridging chlorines is trans to both terminal imido groups and the W–W distance is 2.695(1)Å.